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A blower motor question

07-25-2007, 07:31 PM

Seems like it's my week here asking questions.

I have a furnace blower motor (110v) mounted to a wood stand that I use to move air in my shop. I've had it for years and years. I recently read that running them without any kind of duct extension will make them run hotter than needed and not blow as good. Is this true? I read that just a 6" long square extension to the outlet will make it work better and cooler. Is this true? Inquiring minds want to know.

Mark

Congratulations to Mr. "the sky is falling" Al Gore, nominated the new Village Idiot!

I have a furnace blower motor (110v) mounted to a wood stand that I use to move air in my shop. I've had it for years and years. I recently read that running them without any kind of duct extension will make them run hotter than needed and not blow as good. Is this true? I read that just a 6" long square extension to the outlet will make it work better and cooler. Is this true? Inquiring minds want to know.

Mark

Most squirrel cage fans need some type of back pressure to prevent them from free-wheeling. The back pressure will slow the fan down but increase the CFM and make it run cooler. You could probably test the efficiency of the fan yourself by sliding a piece of plywood over the outlet of the fan while watch an amprobe on the electrical to the fan.

Comment

I'm still confused. The blower is open on both sides for inlet air with one square opening for exiting air. If I close off both inlets, it spins much faster, because I guess there is no air going into the blower, hence no load. So you are saying to partially block off one side of the inlet to get more air flow? Hmm, my mind can't seem to rationalize that one. But it's also late and i'm tired.
I don't have an amp probe either. Rats! Oh well. I'll fiddle with it tomorrow and see what happens. It's been doing fine for atleast 10 years now, guess it will do ok until it finally dies! (kinda like ME!LOL)

Mark

Congratulations to Mr. "the sky is falling" Al Gore, nominated the new Village Idiot!

Comment

As you noticed, when you cover the intake the motor spins faster without the load, if you had an amp meter you would notice the current decreasing.
The idea is to restrict the input to allow the motor to spin faster with less load to produce the same CFM at a higher air speed. You almost need a CFM gauge and amp meter to tune it perfectly but running as is will (and has) work fine